U.S. patent number 4,839,322 [Application Number 07/065,159] was granted by the patent office on 1989-06-13 for high surface area polymers of pyrrole or copolymers of pyrrole.
This patent grant is currently assigned to The Lubrizol Corporation. Invention is credited to Richard Yodice.
United States Patent |
4,839,322 |
Yodice |
June 13, 1989 |
**Please see images for:
( Certificate of Correction ) ** |
High surface area polymers of pyrrole or copolymers of pyrrole
Abstract
Polymers of pyrrole or copolymers of pyrrole are obtained having
high surface area and low conductivity. Such polymers and
copolymers are useful in forming catalysts.
Inventors: |
Yodice; Richard (Willoughby,
OH) |
Assignee: |
The Lubrizol Corporation
(Wickliffe, OH)
|
Family
ID: |
26745280 |
Appl.
No.: |
07/065,159 |
Filed: |
June 24, 1987 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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859571 |
May 5, 1986 |
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Current U.S.
Class: |
502/159;
205/419 |
Current CPC
Class: |
B01J
31/06 (20130101); B01J 31/1658 (20130101); B01J
31/181 (20130101); C08G 61/124 (20130101); B01J
2231/4205 (20130101); B01J 2231/60 (20130101); B01J
2531/16 (20130101); B01J 2531/72 (20130101); B01J
2531/842 (20130101) |
Current International
Class: |
B01J
31/06 (20060101); B01J 31/26 (20060101); C08G
61/12 (20060101); C08G 61/00 (20060101); C25B
003/02 (); B01J 031/06 () |
Field of
Search: |
;204/59R,72
;502/101,162,167,509,152,153,150,159 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Niebling; John F.
Assistant Examiner: Hsing; Ben C.
Attorney, Agent or Firm: Collins; Forrest L. Cordek; James
L. Tritt; William C.
Parent Case Text
This is a continuation of co-pending application Ser. No. 859,571
filed on May 5, 1986, now abandoned.
Claims
What is claimed is:
1. A pulverant catalytic composition comprising a polymer of
pyrrole a copolymer of pyrrole and mixtures thereof obtained by
treating pyrrole or a co-polymerizable mixture containing a pyrrole
at an electronically conductive surface in an electrolytic bath
comprising the steps of:
(A) immersing an electronically conductive surface in an
electrolytic bath comprising at least one liquid and at least one
non-miscible liquid or gas or finely divided solid particles
wherein a pyrrole or co-polymerizable mixture containing a pyrrole
is one of the liquids or is dissolved in at least one of the
liquids, and
(B) passing an electric current through said bath at a voltage
sufficient to electropolymerize the pyrrole or co-polymerizable
mixture containing a pyrrole at the electronically conductive
surface thereby obtaining the polymer of pyrrole or copolymer of
pyrrole,
(C) treating the of polymer pyrrole or copolymer of pyrrole in the
presence of a strong base to substantially increase the surface
area of, and substantially deprotonate the polymer of pyrrole or
copolymer of pyrrole, and
(D) reacting the high surface area polymer of pyrrole or copolymer
of pyrrole with a catalytic active material.
2. The composition of claim 1 wherein the catalytic active material
is a Friedel Crafts catalyst.
3. The composition of claim 1 wherein the catalytic active material
is an oxygen reduction catalyst.
4. The composition of claim 3 wherein the catalytic active material
is a transition metal.
5. The composition of claim 1 wherein the surface area of the
polymer of pyrrole or copolymer of pyrrole prior to contact with
the catalytic active material is at least about 25 square meters
per gram.
6. The composition of claim 1 wherein the catalytic active material
is selected from the group consisting of ferric, ferrous, cupric,
cuprous, manganic, nickel, osmium, ruthenium and aluminum ions and
mixtures thereof.
7. The composition of claim 1 wherein the catalytic active material
is selected from the group consisting of bromine, iodine, boron
triflouride, and sulfur trioxide.
8. The composition of claim 1 wherein the polymer of pyrrole or
copolymer of pyrrole is reprotonated.
9. The composition of claim 8 wherein the composition is
reprotonated with a non-oxidative acid.
10. The composition of claim 9 wherein the composition is
reprotonated with a mineral acid selected from the group consisting
of phosphoric, sulfuric, and hydrochloric or mixtures thereof.
11. The composition of claim 8 wherein the composition is
reprotonated with quinone sulfonic acid or methane sulfonic
acid.
12. The composition of claim 1 wherein the polymer of pyrrole or
copolymer of pyrrole is polymerized in the presence of one or more
low mobility anions.
13. The composition of claim 12 wherein the low mobility anions are
selected from the group consisting of the sulfates and sulfonates
of alkyl, aryl, arylalkyl, alkaryl or polyolefin sulfates or
sulfonates.
14. The composition of claim 1 wherein the strong base is selected
from the group consisting of alkali metal and alkaline earth metal
hydroxides, alkoxides and amine bases.
15. A process for preparing a pulverant catalytic composition
comprising a polymer of pyrrole or a copolymer of pyrrole and
mixtures thereof obtained by treating a pyrrole or a copolymerizabe
mixture containing a pyrrole at an electronically conductive
surface in an electrolytic bath comprising the steps of:
(A) immersing an electronically conductive surface in an
electrolytic bath comprising at least one liquid and at least one
non-miscible liquid or gas or finely divided solid particles
wherein a pyrrole or co-polymerizable mixture containing a pyrrole
is one of the liquids or is dissolved in at least one of the
liquids, and
(B) passing an electric current through said bath at a voltage
sufficient to electropolymerize the pyrrole or co-polymerizable
mixture containing a pyrrole at the electronically conductive
surface thereby obtaining the polymer of pyrrole or a copolymer of
pyrrole,
(C) treating the polymer of pyrrole or copolymer of pyrrole in the
presence of a strong base to substantially increase the surface
area of, and substantially deprotonate the polymer of pyrrole or
copolymer of pyrrole, and
(D) reacting the high surface area polymer of pyrrole or copolymer
of pyrrole with a catalytic active material, thereby forming the
catalytic composition.
16. The process of claim 15 wherein the catalytic active material
is a Friedel Crafts catalyst.
17. The process of claim 15 wherein the catalytic active material
is an oxygen reduction catalyst.
18. The process of claim 17 wherein the catalytic active material
is a transition metal.
19. The process of claim 15 wherein the surface area of polymer of
pyrrole or copolymer of pyrrole prior to contact with the catalytic
active material is at least about 25 square meters per gram.
20. The process of claim 15 wherein the catalytic active material
is selected from the group consisting of ferric, ferrous, cupric,
cuprous, manganic, nickel, osmium, ruthenium and aluminum ions and
mixtures thereof.
21. The process of claim 15 wherein the catalytic active material
is selected from the group consisting of bromine, iodine, boron
triflou and sulfur trioxide.
22. The process of claim 15 wherein the polymer of pyrrole or
copolymer of pyrrole is reprotonated.
23. The process of claim 22 wherein the polymer of pyrrole or
copolymer of pyrolle is reprotonated with a mineral acid selected
from the group consisting of phosphoric, sulfuric, and hydrochloric
or mixtures thereof.
24. The process of claim 22 wherein the composition is reprotonated
with quinone sulfonic acid or methane sulf acid.
25. The process of claim 15 wherein the polymer of pyrrole or
copolymer of pyrrole is polymerized in the presence of one or more
low mobility anions.
26. The process of claim 25 wherein the low mobility anions are
selected from the group consisting of the sulfates and sulfonates
of alkyl, aryl, arylalkyl, alkaryl or polyolefin sulfates or
sulfonates.
27. The process of claim 15 wherein the strong base is selected
from the group consisting of alkali metal and alkaline earth metal
hydroxides, alkoxides and amine bases.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention describes materials formed from pyrrole or
copolymers of pyrrole exhibiting high surface area.
2. Description of the Art
It is known that polymers of pyrrole and copolymers of pyrrole may
be obtained as electronically conducting organic polymers. Such
materials have been known to have conductivities exceeding 1
ohm.sup.-1 cm.sup.-1. It is further known that materials of a
similar class include polyacetylene, poly-p-phenylene,
poly-p-phenylene sulfide, polyaniline and poly (2,5
thienylene).
Pyrrole black, a polymeric powdered material formed by oxidizing
pyrrole in homogeneous solution (e.g. with H.sub.2 O.sub.2) has
been known for many years. Gardini, Adv. Heterocycl. Chem, 15,
67(1973). An electrochemical method of producing polypyrrole as a
powdery film on an electrode has been reported. A. Dall' olio et
al., Comp. Rend., 433, 267c (1968). Electropolymerization to
produce polymer films from pyrrole has been reported. Diaz et al,
J. Chem. Soc, Chem. Comm., 635, (1979)(hereinafter Diaz (I)); Diaz
et al, J. Chem. Soc. I, Chem. Comm., 397, (1980) (hereinafter Diaz
(II)); Diaz, Chemica Scripta, 17, 45, (1981) (hereinafter Diaz
(III)); and Kanazawa et al., J. Chem. Soc., Chem. Comm., 954 (1979)
(hereinafter Kanazawa (I)). Electropolymerized polypyrrole from
substituted pyrroles has been reported. Diaz (II); Diaz et al., J.
Electroanal Chem., 129, 115, (1981) (hereinafter Diaz (IV)); Diaz
et al., J. Electroanal Chem., 130, 181, (1981) (hereinafter Diaz
(V)). Co-polymer films produced by electropolymerizing mixtures of
pyrrole and substituted pyrrole have also been reported. A mixture
of pyrrole and N-methyl pyrrole has been polymerized and it is
believed that both monomers are incorporated into the polymer. Diaz
(II); Diaz, Proc. Int. Conf. on Low Dimensional Synthetic Metals
Chemica Scripta, 17, 0000, (1981) (hereinafter Diaz (VI; and
Kanazawa et al J. Synth Metals, 4, 119, (1981) (hereinafter
Kanazawa (II)).
Polypyrrole is electronically conducting in the charged or oxidized
state (black), and is produced in this state by
electropolymerization. When completely reduced to the neutral or
discharged state (yellow), it is an electronic insulator. The
electropolymerized polypyrrole is produced in the oxidized, i.e.
conductive, state and (unlike other conducting polymers such as
polyacetylene) does not require any subsequent chemical or
electrochemical treatment to increase its conductivity above 1
ohm.sup.-1 cm.sup.-1. A counter-anion is incorporated into the
material during the electropolymerization process to balance the
positive charge on the polymer backbone. Diaz (III).
Polypyrrole can also be electropolymerized as a continuous film on
electrodes. The highest electronic conductivities reported for the
continuous films are of the order of about 100 ohm.sup.-1
cm.sup.-1. Diaz (I); Kanazawa et al., Syn. Metals, 329, (1980)
(hereinafter Kanazawa (III)). These conductivities can be orders of
magnitude lower depending on the counter-anion incorporated.
A large number of counter-anions have been used, including
BF.sub.4.sup.-, PF.sub.6.sup.-, AsF.sub.6.sup.-, ClO.sub.4.sup.31,
HSO.sub.4.sup.-, CF.sub.3 SO.sub.3.sup.-, CH.sub.3 C.sub.6 H.sub.4
SO.sub.3.sup.31 , CF.sub.3 COO.sup.-, HC.sub.2 O.sub.4.sup.-,
Fe(CN).sub.6.sup.3-. Diaz (IV); Diaz (VI); Kanazawa (I); and Noufi
et al, J. Electrochem. Soc., 128 2596, (1981).
N-substituted pyrroles have been polymerized, including methyl,
ethyl, n-propyl, n-butyl, isobutyl and phenyl and substituted
phenyl pyrroles. Diaz (IV); Diaz et al., Electrochemical Society
Extended Abstracts, Vol. 82-1. Abstract No. 617, (1982)
(hereinafter Diaz (VII)). These materials have reported electronic
conductivities orders of magnitude lower than polypyrrole itself.
Kanazawa (II); Diaz (VII). It has been reported that
beta-substituted pyrroles such as 3,4 dimethyl pyrrole have been
polymerized. Gardini, supra.
The polymers have been prepared to date with non-aqueous solvents,
typically acetonitrile, (Diaz (I); Diaz (II); and Diaz (VI)),
containing a dissolved salt which provides the counter-anion. It is
known that the physical properties of the resulting films are
sensitive to the formation conditions. For example, in
acetonitrile, small traces of water in the solvent produce a film
with a smoother surface than that produced in anhydrous
acetonitrile. Diaz (VI). The polypyrrole tetrafluoroborate films
produced by Diaz et al. are continuous, space-filling and very
poorly crystalline with a density of 1.48 g cm.sup.-3. Kanazawa
(III).
Polypyrrole films are thermally stable at room temperature and are
insoluble in common solvents. Diaz (I); Kanazawa (II); and
Tourillon et al., Electrochemical Society Extended Abstracts, Vol.
82-1, Abstract No. 618, (1982). Polypyrrole in the oxidized form is
reported to be chemically stable in ambient conditions of O.sub.2
and moisture for several months. Diaz et al., J. Electroanal.
Chem., 121, 355, (1981) (hereinafter Diaz (VIII)); Watanabe et al,
Bull. Chem. Soc. Jpn., 54, 2278, (1981). Polypyrrole fluoroborate
films have been shown to be unstable under oxidative conditions
such as potentials greater than +0.6 v. (SCE) or in the presence of
halogens. Bull et al, J. Electrochem. soc., 129, 1009. (1982).
Polypyrrole can be driven repeatedly between the conducting and
non-conducting state. Bull et al, supra; Diaz et al, "Conducting
Polymers", Polymer Sci. & Technology, p. 149 et. seq., Plenum
Press, N.Y., (1981) (hereinafter Diaz (IX)). Rapid complete
switching is reported to require the use of thin films (i.e., less
than about 0.1 micrometer) and switching is difficult for
thicknesses greater than about 1 micrometer. Diaz (II); Diaz (IX).
It has been shown that although a film may contain BF.sub.4.sup.-
counter-anions when it is formed (i.e., is the charged state),
BF.sub.4.sup.- is no longer present in the film when it is in the
neutral (i.e., reduced or discharged) state. Diaz (IV). It has been
suggested that both the anion and the cation of the electrolyte
salt affect ion diffusion during reduction and oxidation of
polypyrrole films. Diaz (IV).
Polymers have been produced with different degrees of oxidation,
depending on the anion and/or substituents. Most of these materials
have degrees of oxidation around 0.25 (i.e., one quarter of the
polymer rings are oxidized). In an article entitled "Proton
Modification of Conducting Polypyrrole", J. Phys. Chem. Solids,
Volume 48, No. 4, pages 427-432, Inganaes et al reported that the
deprotonation of polypyrrole may be accomplished through the use of
caustic.
It is not currently known that a polymer of pyrrole or copolymer of
pyrrole can be made having a significantly higher surface area. It
is highly desirable to have a high surface polymer which is
essentially nonreactive as it may be used as a catalyst support
such as for a Friedel Crafts catalyst or an oxygen reduction
electrode.
It has been found that by treating the polymers, for instance,
which are obtained according to U.S. Ser. No. 460,695 filed on Jan.
24, 1983 now abandoned that suitable precursors for high surface
area polymers may be obtained. Specifically, it has been found that
the processing in the aforementioned application allows for the
polymers of pyrrole or copolymers of pyrrole to be deprotonated
thereby rendering an extremely high surface area polymer which is
suitable as a catalyst support.
Throughout the specification and claims, percentages and ratios are
by weight; temperatures are in degrees Celsius and pressures are in
KPa over ambient unless otherwise indicated. The references cited
herein are specifically incorporated by reference to the extent
applicable.
SUMMARY OF THE INVENTION
This invention describes a high surface area polymeric organic
semi-conductor obtained from the group consisting of pyrrole and
copolymers of pyrrole and mixtures thereof.
A further aspect of the invention is a polymeric organic
semi-conductor obtained from the group consisting of pyrrole and a
copolymer of pyrrole and mixtures thereof having a surface area
greater than 25 square meters per gram.
An additional aspect of the invention is a catalytic composition
comprising a polymer of pyrrole or a copolymer of pyrrole and
mixtures thereof obtained by treating pyrrole or a co-polymerizable
mixture containing a pyrrole at an electronically conductive
surface in an electrolytic bath comprising the steps of:
(A) immersing an electronically conductive surface in an
electrolytic bath comprising at least one liquid and at least one
non-miscible liquid or gas or finely divided solid particles
wherein a pyrrole or co-polymerizable mixture containing a pyrrole
is one of the liquids or is dissolved in at least one of the
liquids, and
(B) passing an electric current through said bath at a voltage
sufficient to electropolymerize the pyrrole or co-polymerizable
mixture containing a pyrrole at the electronically conductive
surface thereby obtaining the polymer of pyrrole or copolymer of
pyrrole,
(C) treating the polymer of pyrrole or copolymer of pyrrole in the
presence of a strong base to substantially increase the surface
area of the polymer of pyrrole or copolymer of pyrrole, and
(D) introducing to the high surface area polymer of pyrrole or
copolymer of pyrrole a catalytic active material.
Also described herein is a process for preparing a catalytic
composition comprising a polymer of pyrrole or a copolymer of
pyrrole and mixtures thereof obtained by treating a pyrrole or a
copolymerizable mixture containing a pyrrole at an electronically
conductive surface in an electrolytic bath comprising the steps
of:
(A) immersing an electronically conductive surface in an
electrolytic bath comprising at least one liquid and at least one
non-miscible liquid or gas or finely divided solid particles
wherein a pyrrole or co-polymerizable mixture containing a pyrrole
is one of the liquids or is dissolved in at least one of the
liquids, and
(B) passing an electric current through said bath at a voltage
sufficient to electropolymerize the pyrrole or co-polymerizable
mixture containing a pyrrole at the electronically conductive
surface thereby obtaining the polymer of pyrrole or a co-polymer of
pyrrole,
(C) treating the polymer of pyrrole or co-polymer of pyrrole in the
presence of a strong base to substantially increase the surface
area of the polymer of pyrrole or copolymer of pyrrole, and
(D) introducing to the high surface area polymer of pyrrole or
copolymer of pyrrole a catalytic active material, thereby forming
the catalytic composition.
Yet a further embodiment is a process for preparing a catalytic
composition comprising a polymer of pyrrole or a copolymer of
pyrrole and mixtures thereof obtained by treating a pyrrole or a
copolymerizable mixture comprising the steps of:
(a) obtaining a pyrrole or a copolymerizable mixture containing a
pyrrole;
(b) introducing to the pyrrole or copolymerizable mixture
containing a pyrrole a peroxide;
(c) reacting the mixture of the pyrrole or copolymerizable mixture
containing a pyrrole and the peroxide for a sufficient amount of
time to polymerize the pyrrole or the copolymerizable mixture
containing a pyrrole,
(d) treating the polymer of pyrrole or copolymer of pyrrole in the
presence of a strong base to substantially increase the surface
area of the polymer of pyrrole or copolymer of pyrrole, and
(e) introducing to the high surface area polymer of pyrrole or
copolymer of pyrrole a catalytic active material, thereby forming
the catalytic composition.
DETAILED DESCRIPTION OF THE INVENTION
This invention, as previously noted, describes high surface area
polymers of pyrrole or copolymers of pyrrole which are useful as
catalysts support. The term "pyrrole" as used herein describes a
material of the formula given below: ##STR1##
In the drawing above, R.sup.1, R.sup.3, and R.sup.4 are all
independently hydrogen or hydrocarbyl and R.sup.2 and R.sup.5 are
always hydrogen. If R.sup.1 is other than hydrogen, then a
copolymerizable material containing hydrogen at the 1-position must
also be employed.
The term "pyrrole" thus includes materials which may be substituted
at the three and/or four positions on the pyrrole molecule. A
preferred material for use herein is the unsubstituted pyrrole,
that is, the compound containing only carbon, nitrogen and hydrogen
atoms. Copolymers of pyrrole include any material which may be
condensed with pyrrole through the two positions which are alpha to
the nitrogen atom in the pyrrole molecule thereby giving a
structure favoring electron distribution throughout the molecule.
Shown as compound (B) below is a repeating polymeric unit formed
from pyrrole. ##STR2##
In B, and C, infra, the value X.sup.- is an anion such as the low
mobility anion described herein.
Where a substituted pyrrole is intended, it is desirable that the
substitution be of a non-electrophillic group. In particular,
normal alkyls such as methyl, ethyl or propyl are useful. It is
preferred, however, that the pyrrole be a non-substituted pyrrole.
When substitution is present, it is preferred that the substitution
be the beta, beta-disubstituted pyrrole.
Where copolymers of pyrrole are utilized, it is desirable that the
pyrrole structure be the prominent material within the copolymer.
Thus, the molar ratio ratio of the pyrrole to the copolymer should
be at least 1:l, and preferably greater than 2:1. A particularly
preferred material for use as a copolymer with pyrrole is thiophene
as shown in formula (C). ##STR3##
The surface area of the polymers as measured by the BET nitrogen
method. The polymers obtained herein after deprotonation and prior
to being loaded with the catalyst should have a surface area
greater than 20 square meters per gram, preferably greater than 25
square meters per gram and most preferably greater than 50 square
meters per gram. The upper limit on the surface area of the
polymers is not particularly important other than that the polymer
should not be so high in surface area as to be a fine powder which
can not support the catalyst. Even this problem may be solved by
providing the finely powdered polymer with an additional catalyst
support such that the polymer of pyrrole or copolymer of pyrrole is
merely retaining the catalyst while another support material
retains the polymer of pyrrole or copolymer of pyrrole.
Thus, the desirable effective range for the polymer of pyrrole or
copolymer of pyrrole will be from about 20 square meters per gram
to about 1000 square meters per gram, preferably from about 50
square meters per gram to 750 square meters per gram.
There are two main methods of obtaining the polymer of pyrrole or
copolymer of pyrrole of the present invention having a sufficient
area to function as a catalyst support. These two methods are the
preparation of the polymer by electrodeposition or through chemical
means, e.g., a peroxide system. The polymers are then treated with
base to increase the surface area of the polymer to the necessary
degree.
An alternative method of preparing the pyrrole for use in the
present invention is the use of a free radical mechanism to obtain
the polypyrrole or copolymer of pyrrole. For instance, a material
such as potassium persulfate (K.sub.2 S.sub.2 O.sub.8) is used to
generate a free radical of potassium persulfate. Other similar
peroxygen systems may be used to polymerize the pyrrole. The
persulfate is conveniently employed at a level of about 3 moles to
1 mole of the pyrrole. The reaction temperature for obtaining the
pyrrole or co-polymer of pyrrole through the peroxygen method is at
about 10.degree. C. to about 50.degree. C.., preferably about
15.degree. C. to about 30.degree. C.
The peroxygen produced polymer of pyrrole or co-polymer of pyrrole
is quite similar to the electrochemically produced polymer of
pyrrole or co-polymer of pyrrole. A notable exception is that the
peroxygen produced material gives a BET surface area, slightly
greater for the polymer of pyrrole or co-polymer of pyrrole. It is
further noted, however, that following deprotonation, the polymer
of pyrrole or co-polymer of pyrrole obtained from the peroxygen
method will not achieve as great a BET surface area as the
deprotonated polymer of pyrrole or co-polymer of pyrrole obtained
from the electrochemical process.
A preferred method of making the polymer of pyrrole or copolymer of
pyrrole which is ultimately useful as a catalyst support is
described in Bundesrepublik Deutschland Offenlegungsschrift 34 021
133 A1 dated July 26, 1984, to Gerdes et al, herein incorporated by
reference. The materials of Gerdes are electrically conducting
polymers of pyrrole or copolymers of pyrrole. These materials are
generally obtained by electropolymerization of pyrrole or a
copolymerizable mixture containing pyrrole at an electronically
conductive surface in an electrolytic bath.
The method of Gerdes et al comprises the steps of:
(A) immersing an electronically conductive surface in an
electrolytic bath comprising at least one liquid and at least one
non-miscible liquid or gas or finely divided solid particles
wherein the pyrrole or the copolymerizable mixture containing a
pyrrole is one of the liquids or is dissolved in at least one of
the liquids, and (B) passing an electric current through said bath
at a voltage sufficient to electropolymerize the pyrrole or
copolymerizable mixture containing a pyrrole at the electronically
conductive surface. In a preferred embodiment of this method the
electrolytic bath comprises an aqueous mixture comprising pyrrole,
or mixture of pyrrole and a copolymerizable monomer and water. The
invention further provides for an electrochemical cell comprising
polymeric electrode means, said polymeric electrode means being
positive and/or negative and comprising electronically conducting
polypyrrole or a co-polymer of pyrrole prepared in accordance with
the foregoing method.
Further provided by Gerdes et al is a method of preparing
electronically conducting polypyrrole or a co-polymer of pyrrole
which comprises the steps of: (A) electropolymerizing a pyrrole or
a copolymerizable mixture of a pyrrole at an electronically
conductive surface in an electrolytic bath by (1) immersing an
electronically conductive surface in an electrolytic bath which
comprises (a) an aqueous dispersion of a pyrrole, or a mixture of
said aqueous dispersion and at least one copolymerizable monomer or
(b) a pyrrole or a mixture of a pyrrole and/or at least one
copolymerizable monomer, water and a water-immiscible diluent, (2)
agitating the bath, and (3) passing an electric current through
said bath at a voltage sufficient to electropolymerize the pyrrole
or pyrrole mixture and deposit the polymer or co-polymer on the
electronically conductive surface, and (B) removing said polymer or
co-polymer from the conductive surface. In a preferred embodiment
of this method, the electrolytic bath comprises an aqueous mixture
comprising pyrrole or a copolymerizable mixture of pyrrole, water,
and one or more low mobility anions which are incorporated into the
polypyrrole by electropolymerization and which anions are
characterized by an average ionic transference number for said low
mobility anions on reduction of less than about 0.1. The invention
further provides for an electrochemical cell comprising polymeric
electrode means, said polymeric electrode means being positive
and/or negative and comprising polypyrrole or a co-polymer of
pyrrole prepared in accordance with the foregoing method.
There is further described herein a method of preparing
electronically conducting polypyrrole or a co-polymer of pyrrole
which comprises electropolymerization of a pyrrole or a
copolymerizable mixture containing a pyrrole at an electronically
conductive surface in an electrolytic bath by (A) immersing an
electronically conductive surface in an electrolytic bath
comprising (i) a pyrrole or a mixture of a pyrrole with a
copolymerizable monomer, (ii) one or more low mobility anions which
are incorporated into the polypyrrole or co-polymer of pyrrole and
which are characterized by an average ionic transference number for
said low mobility anions during reduction of the polypyrrole or
co-polymer of less than about 0.1, and (iii) an organic diluent,
and (B) passing an electric current through said bath at a voltage
sufficient to electropolymerize the pyrrole or copolymerizable
mixture containing pyrrole at the electronically conductive
surface.
The electronically conducting compositions of the invention contain
at least one low mobility anion, A, which has a strong tendency to
be retained in the composition on reduction. The transport of ionic
charge to compensate the change oxidation state of the polymer is
then carried out principally by ions of the electrolyte in which
the redox process is carried out. The low mobility anions may be
characterized by their ionic transference numbers. The ionic
transference number is defined as the fraction of the ionic current
carried by the particular anion averaged over substantially full
reduction of the composition. The polymer is formed in the oxidized
state (black) which is electronically conductive and can be reduced
to the neutral state (yellow) which is insulating. However, for
practical purposes, the reduction of thick (500 millimicron or
greater) films does not proceed to completion even at very negative
potentials. The material remains black in appearance and retains
some electronic conductivity although above about 90% reduction its
resistance may increase. In general, the low mobility anions
utilized in the compositions of this invention will be
characterized by an average ionic transference number for said low
mobility anions during reduction of less than 0.1 and preferably
less than about 0.05. A most preferred low mobility anion is one
characterized by an average ionic transference number for said low
mobility anions during reduction of less than 0.01.
These transference numbers may be determined by elemental analysis
of the polymers before and after reduction. Thus, the transference
number (t.sub.A) of the low mobility anion may be defined as
follows:
wherein (N.sub.A).sub.O is the number of moles of the charge
compensating anion initially in the polymer (when it is in the
oxidized state) and delta N.sub.A is the change in the number of
moles of the anion after substantially full reduction (towards the
neutral state).
The porous compositions of the invention also are characterized by
an apparent density of from about 0.01g cm.sup.-3 up to about the
bulk density of the polypyrrole or copolymer of pyrrole.
Bulk or theoretical density of the polymers is the density of
continuous, pure polymer containing no voids, pores, cavities or
inclusions. The bulk or theoretical density can usually be
determined by flotation methods. Apparent density for less dense
forms of the polymer such as the porous materials is defined from
the mass of the polymer and the volume calculated from the external
dimensions of the material. Since voids, cavities, etc., are
included in the porous-type materials, their apparent density will
be lower than the bulk density.
The porous composition of the invention also is characterized as
having an electrochemically accessible surface area of at least two
times the surface area of a smooth film of bulk density of the
polymer or co-polymer. Preferred materials have significantly
greater surface areas, (e.g., 1000 times or more than that of a
smooth film of bulk density).
The electronically conducting compositions of the present invention
comprise either polypyrrole(s) or co-polymer(s) of pyrrole which
may be obtained by (a) polymerizing mixtures of a pyrrole with
other co-polymerizable monomers or by (b) grafting a co-monomer(s)
to a polpyrrole polymer or by (c) grafting a pyrrole monomer(s) to
a preformed polymer based on a monomer other than pyrrole.
The pyrrole monomers which can be electropolymerized may be pyrrole
or substituted pyrroles such as the C-substituted pyrroles as
described more fully below. Homopolymers of these pyrroles, and
preferably the homopolymers of unsubstituted pyrrole are
included.
Co-polymers of a pyrrole can be prepared, for example, by
polymerizing a mixture of pyrrole and one or more substituted
pyrroles which may be substituted either on the nitrogen atom or at
one or more of the ring carbon atoms in the beta position.
Preferably, the substituent is a lower alkyl group containing from
1 to 7 carbon atoms, and it is more preferably a methyl group.
Thus, for example, co-polymers of pyrrole and N-methylpyrrole or
3,4-dimethyl pyrrole can be prepared in accordance with the methods
of the invention. Alternatively, pyrrole can be co-polymerized with
other heterocyclic ring compounds including those containing
nitrogen (e.g., pyridine, aniline, indole, etc.), furan and
thiophene or with other aromatic or substituted aromatic compounds.
It is necessary that the polymer not consist entirely of an
N-substituted pyrrole as the homopolymers are not capable of being
deprotonated.
The low mobility anions which are incorporated into the
compositions of the invention may be either organic or inorganic
anions. Examples of low mobility inorganic anions useful in the
present invention include transition metal complexes such as
ferricyanide, nitroprusside, iron/sulfur cluster compounds such as
the redox centers of the rubredoxins and the ferredoxins, boron
cluster compounds, cobalt hexacyanide, other transition metal
cyanide complexes, nitroprusside complexes, and other transition
metal oxy complexes or sulfides or chalcogenide complexes, e.g.
WO.sub.4.sup.-, MoO.sub.4.sup.-, Mo(CN)8.sup.4-, Fe.sub.4 S.sub.4
C.sub.4 H.sub.12.sup.-, CrO.sub.4.sup.-, etc.
Preferably, the low mobility anions included in the compositions of
the present invention are organic anions. Examples of organic
anions include those derived from organic sulfates or sulfonates,
and these may be alkyl, cycloalkyl, aryl, arylalkyl or alkaryl
sulfates and sulfonates. The anions which are useful in the present
invention may contain more than one anionic site, i.e., more than
one ionizable group per molecule, e.g. more than one sulfonic acid
group per molecule. The sulfonates and sulfates useful as the low
mobility anions in the compositions of the present invention may be
represented by the following formulas:
In the above formulas, R.sup.1 is an aliphatic or an aliphatic
substituted cycloaliphatic hydrocarbon or an essentially
hydrocarbon group generally free from unsaturation and usually
containing up to about 30 carbon atoms although it may be polymeric
and contain more than 30 carbon atoms. When R.sup.1 is aliphatic,
it usually contains at least about 4 carbon atoms, and when R.sup.1
is alkyl substituted cycloaliphatic, the alkyl substituents
preferentially contain from 1 to 4 carbon atoms. Specific examples
of R.sup.1 include butyl, hexyl, octyl, lauryl, cetyl, octadecyl
and groups derived from petroleum, saturated and unsaturated
paraffin wax, and olefin polymers including polymerized
mono-olefins and diolefins containing from 2 to about 8 carbon
atoms per olefinic monomer unit. R.sup.1 can also contain other
substituents such as phenyl, cycloalkyl, hydroxy, mercapto, halo,
nitro, amino, lower alkoxy, lower alkyl-mercapto, carbalkoxy, oxo
or thio, or interrupting groups such as --NH--, --O--, --S--, but
preferably its overall hydrocarbon character is retained.
R.sup.2 generally is a hydrocarbon or essentially hydrocarbon group
containing from 1 to about 30 carbon atoms, although it may be
polymeric and contain more than 30 carbon atoms. R.sup.2 is
preferably an aliphatic hydrocarbon group such as alkyl, alkenyl,
or alkylaryl. R.sup.2 also may contain substituents such as those
enumerated above, including the above indicated interrupting
groups, provided the essentially hydrocarbon character thereof is
retained.
The group T in the above formulas V and VI is a cyclic nucleus
which may be derived from an aromatic hydrocarbon such as benzene
or from a heterocyclic compound such as pyridirne. Ordinarily, T is
an aromatic hydrocarbon nucleus and especially benzene. The
subscript and superscript x represents the average number of
ionized groups per molecule. The anion may contain additional
sulfate or sulfonate groups which are not ionized but associated
with some cationic species. In Formulas I through VI, x may have a
value of up to 1000 or more when R.sup.1 or R.sup.1 is polymeric,
but is preferably from 1 to 10, more preferably from 1 to 6, and
generally is 1. The subscript y in Formulas V and VI is a number
ranging from 1 to 5 and preferably is 1.
Anionic compounds containing the anions represented above by
Formulas I through VI are available commercially or can be prepared
readily by techniques known in the art. Examples are salts with
alkali or alkaline earth metals, or ammonium salts.
Examples of sulfonates useful in the invention include the anions
of the following acids; hexyl sulfonic acid, octyl sulfonic acid,
dodecyl sulfonic acid, octyldecyl sulfonic acid, lauryl sulfonic
acid, mahogany sulfonic acid, paraffin wax sulfonic acid, benzene
sulfonic acid, napthalene sulfonic acid, lauryl cyclohexyl sulfonic
acid, dodecyl benzene sulfonic acid; polyethylene sulfonic acids of
various molecular weights; polystyrene sulfonic acids of various
molecular weights, etc. Styrene maleic anhydride co-polymers
bearing sulfonate groups on the rings or styrene maleic anhydride
co-polymers which have been partially or fully converted to the
corresponding imide sulfonates are also useful anionic species in
the invention; such materials are derived from styrene maleic
anhydride co-polymers typically having inherent viscosity of about
0.06 to about 1, preferably about 0.06 to about 0.3 dl g.sup.-1
measured at 30.degree. C. in acetone, 0.4-1 g dl.sup.-1.
A preferred embodiment includes anions derived from aliphatic
compounds containing two sulfonic acid groups and may be
represented by the formula
wherein n is an integer from about 2 to 20 or more and preferably
about 2 to 12. These disulfonic acid salts can be prepared by
techniques known in the art such as by the reaction of alkylene
dihalides with sodium sulfite. Specific examples of such compounds
include the salts of ethane disulfonic acid, 1,4-butane disulfonic
acid, 1,5-pentane disulfonic acid, 1,6- hexane disulfonic acid,
1,8-octane disulfonic acid and 1,10-decane disulfonic acid.
Examples of sulfates which are useful include alkyl sulfates such
as lauryl sulfate; and polyethylene sulfates of various molecular
weights.
Another class of sulfates which are useful as the low mobility
anions in the compositions of the present invention are
polysulfates polyhydroxy compounds. Such compounds can be obtained
by reacting polyhydroxy compounds with an appropriate reagent such
as chlorosulfonic acid thereby converting one or more of the
hydroxy groups to sulfate groups. Examples of polyhydroxy compounds
which can be used to prepare such polysulfates include
pentaerythritol, mannitol, trimethylolpropane, dipentaerythritol,
etc. As mentioned, one or more of the hydroxy groups in these
polyhydroxy compounds can be sulfated to produce a variety of
products. Ammonium sulfates can be prepared directly from
polyhydroxy compounds by reaction with an aminosulfonic acid in the
presence of a diluent such as dimethyl formamide.
Amido, and preferably acrylamido alkane sulfonic acid anions can be
used in the compositions of the invention. Specific examples of
such anions include: 2,2-bisacrylamido-1,1,-dimethylethanesulfonic
acid anion; 2-acrylamido-2-methyl propane sulfonic acid anion; and
poly(2-acrylamido-2-methyl propane sulfonic acid sodium salt of
various molecular weights.
The low mobility anions included in the compositions of the present
invention may also be derived from pentavalent phosphorous
compounds. Examples of such phosphorous compounds are phosphates,
phosphonates and phosphinates. The phosphorous compounds useful as
the low mobility anions in the compositions of the present
invention may be represented by the following formulas:
In the above formulas R.sup.3 is R.sup.1 or R.sup.1 yT as defined
above, or can be hydrogen, an alkali metal (e.g., lithium, sodium,
potassium, etc.) or an alkaline-earth metal (e.g., calcium,
magnesium, etc.). R.sup.4 is R.sup.2 or R.sup.2 yT, as defined
above, or can be hydrogen, an alkali metal (e.g., lithium, sodium,
potassium, etc.) or an alkaline earth metal (e.g., calcium,
magnesium, etc.). Each of X.sup.1, X.sup.2, X.sup.3 and X.sup.4 is
oxygen or sulfur (e.g., a phosphorus double bond); and each a and b
is 0 or 1. The subscript and superscript z represents the average
number of ionized groups per molecule. In Formulas XI through XIV,
z may be a value of up to 1000 or more when R.sup.1 or R.sup.2 is
polymeric, but is preferably from 1 to 10, more preferably from 1
to 4, and generally is 1. Thus, it will be appreciated that the
pentavalent phosphorous compounds may be for example,
organophosphoric, phosphonic or phosphinic compounds including the
acids, alkali metal salts and alkaline-earth metal salts thereof,
or a thio analog of any of these.
Although useful electronically conducting compositions can be
prepared in accordance with the method of the invention comprising
a polypyrrole or a co-polymer of a pyrrole, and a low mobility
anion as described above, the properties of the compositions may be
improved by the inclusion of other components which provide certain
desirable properties. The electrolytic baths useful in the
formation of the compositions of this invention preferably will
contain a plasticizer. Plasticizers are compounds known in the art
which have the ability when incorporated into polymeric compounds
such as polypyrrole or co-polymers of a pyrrole to increase stretch
elongation and/or decrease the modulus of the polymer and/or
increase flexibility. The last criterion has been used to define
the term plasticizer as applied to the materials in this
application. Compounds which can increase the flexibility of the
compositions of the invention generally are included in the
electrolytic baths. In some instances, the low mobility anions
which are incorporated into the compositions of the invention have
more than one function and may, for example, include the function
of a plasticizer and/or a surface active agent in the composition.
For example, many of the higher molecular weight sulfates or
sulfonates listed above as low mobility anions, also function as
plasticizers and, additionally, can modify the wetting properties
of the polymer. A specific example is sodium lauryl sulfate which
functions as a low mobility anion and as a plasticizer for
polypyrrole and copolymers of pyrrole.
The plasticizers which are useful in the present invention include
organic sulfates or sulfonates such as alkyl, aryl, arylalkyl,
alkaryl and polyolefin sulfates or sulfonates of the types listed
above as low mobility anions. Another class of compounds useful as
plasticizers and the compositions of the present invention are
polyhydroxy compounds.
The polyhydroxy compounds are preferably those containing from 2 to
6 alcoholic radicals of which at least 1 is unsubstituted. The
unsubstituted polyhydric alcohols include ethylene glycol,
1,2-propylene glycol, 1,3-propylene glycol, glycerol, erythritol,
pentaerythritol, arabitol, adonitol, xylitol, mannitol, sorbitol,
and neopentylglycol. Higher molecular weight polyhydric alcohols
include various polyethylene glycols, and polypropylene glycol.
Partially acylated polyhydric alcohols likewise are contemplated
for use herein. The partially acylated polyhydric alcohols are
preferably those containing from 2 to 6 alcoholic radicals of which
at least one but not all are acylated with an aliphatic carboxylic
acid having from about 8 to about 30 carbon atoms. Examples are
glycerol mono-oleate, glycerol di-stearate, sorbitan mono-stearate,
sorbitan di-decanoate, sorbitan tristearate, sorbitan di-behenate,
erythritol mono-oleate, 1,1,1-trimethylol propane mono-myristate,
pentaerythritol di-linoleate, ribitol mono-(9,10-dichloro
stearate), sorbitan mono-oleate, etc.
The polyhydric alcohols may also contain ether linkages within
their molecular structure. The ether-containing polyhydric
alchohols may be obtained by dehydrating a polyhydric alcohol.
Examples of such derivatives are sorbitan and mannitan. The
ether-containing polyhydric alcohols may also be obtained by
reacting a polyhydric alcohol with an epoxide. The expoxides are
for the most part hydrocarbon epoxides and substantially
hydrocarbon epoxides. The hydrocarbon epoxide may be an alkylene
oxide or an aryl-alkylene oxide. The aryl-alkylene oxides are
exemplified by styrene oxide, para-ethylstyrene oxide and
para-chlorostyrene oxide. The alkylene oxides include principally
the lower alkylene oxides such as ethylene oxide, propylene oxide,
1,2-butene oxide and 1,2-hexene oxide. The substantially
hydrocarbon epoxides may contain polar substituents. The polar
substituent is usually a halo radical such as chloro, fluoro,
bromo, or iodo; an ether radical such as methoxy or phenoxy; or an
ester radical such as carbomethoxy. Examples of such epoxides are
epichlorohydrin and butyl, 9,10-epoxy-stearate. The number of ether
linkages in the product is determined by the amount of epoxide
added. Thus it is possible to react polyhydric alcohol such as
sorbitol with 1,2,3 or more equivalents of an epoxide such as
propylene oxide.
The polyhydric alcohols contemplated for use in this invention may
also be ether-containing acylated polyhydric alcohols. These may be
prepared by a number of methods. A polyhydric alcohol may be
dehydrated and subsequently acylated or an alcoholic radical may be
acylated first followed by dehydration of other alcoholic radicals.
As mentioned previously, the ether linkage may also be introduced
by the reaction of an epoxide with the polyhydric alcohol either
before or after acylation. Examples of ether-containing acylated
polyhydric alcohols include polyoxyethylene sorbitan mono-oleate,
polyoxyethylene sorbitan tri-stearate, polyoxyethylene glycerol
di-stearate, polyoxypropylene sorbitan di-linoleate, and
polyoxypropylene pentaerythritol mono-oleate.
A particularly preferred example of a class of plasticizers useful
in the compositions of the invention are polyalkylene polyols,
polyethers and polyglycerols, and particularly polyalkylene glycols
wherein the monomer unit may contain from 1 to about 4 carbon atoms
and preferably about 2 carbon atoms. A specific example is
polyethylene glycol. The molecular weight of the plasticizers may
vary over a wide range depending upon the composition to be
modified and the properties which are to be modified by inclusion
of the plasticizer. Polyethylene glycols of molecular weight of
from about 300 to about 5,000,000 are included in the electrolytic
bath composition and are useful in modifying the properties of the
compositions of the present invention.
It also has been discovered that when the electropolymerization of
pyrrole or polymerizable mixtures of pyrrole is carried out using
either an aqueous medium or a multi-phase system as described
below, the presence of polyethylene glycol over a range of
molecular weights confers mechanical strength and flexibility to
the polymeric compositions obtained. Moreover, when polyethylene
glycol of various molecular weights is added to electrolytic baths
of the invention, the morphology of the polymeric composition
obtained generally can be modified by varying the molecular weight
of the glycol added.
The amount of plasticizer included in the electrolytic bath of the
invention may vary over a wide range, particularly if the low
mobility anion also fuctions as a plasticizer. Generally, however,
the electrolytic bath compositions of the invention will contain
less than about 75% of plasticizer and preferably, less than about
25% by weight of the plasticizer based on the total weight of the
bath composition.
Surface active agents, also variously referred to as wetting agents
or emulsifying agents, may be included in the compositions of the
invention and in the electrolytic baths utilized to form the
compositions of the invention.
The surface active agent may be hydrophilic or hydrophobic.
Typically, the surfactant is a hydrophilic surfactant, and
generally, has an HLB (hydrophilic-lipophilic balance) in the range
of about 10 to about 20.
The surfactant can be of the cationic, anionic, non-ionic or
amphoteric type. Many such surfactants of each type are known to
the art. See, for example, McCutcheon's "Detergents and
Emulsifiers", 1978, North American Edition, published by
McCutcheon's Division, MC Publishing Corporation, Glen Rock, New
Jersey, U.S.A., particularly pages 17-33 which are hereby
incorporated by reference for their disclosures in this regard.
Anionic surfactants contain negatively charged polar groups while
cationic surfactants contain positively charged polar groups.
Amphoteric surfactants contain both types of polar groups in the
same molecule. A general survey of useful surfactants is found in
Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition,
Volume 19, page 507 and following (1969, John Wiley and Son, New
York) and the aforementioned compilation published under the name
of McCutcheon's. These references are both hereby incorporated by
reference for their disclosures relating to cationic, amphoteric
and anionic surfactants. The anionic or non-ionic surfactants are
preferred. The low mobility anion incorporated into the polymer may
additionally perform the function of a surface active agent.
Among the useful anionic surfactant types are the widely known
metal carboxylate soaps, organo sulfates, sulfonates,
sulfocarboxylic acids and their salts, and phosphates. Ueful
cationic surfactants include nitrogen compounds such as amine
oxides and the well known quaternary ammonium salts. Amphoteric
surfactants include amino acid type materials and similar types.
Various cationic, anionic and amphoteric dispersants are available
from the industry particularly from such companies as Rohm and Haas
and Union Carbide Corporation. Among the non-ionic surfactants are
the alkylene oxide-treated products, such as ethylene oxide-treated
phenols, alcohols, esters, amines and amides. Ethylene
oxide/propylene oxide block co-polymers are also useful non-ionic
surfactants. Glycerol esters and sugar esters are also known to be
non-ionic surfactants. A typical non-ionic surfactant class useful
with the derivatives of the present invention are the alkylene
oxide-treated alkyl phenols such as the ethylene oxide alkyl phenol
condensates sold by the Rohm & Haas Company. A specific example
of these is Triton X-100 which contains an average of 9-10 ethylene
oxide units per molecule, has an HLB value of about 13.5 and a
molecular weight of about 628. Many other suitable non-ionic
surfactants are known; see, for example, the aforementioned
McCutcheon's as well as the treatise "Non-ionic Surfactants" edited
by Martin J. Schick, M. Drekker Co., New York, 1967, which is
hereby incorporated by reference for its disclosures in this
regard.
Further information about anionic and cationic surfactants also can
be found in the texts "Anionic Surfactants", Parts II and III,
edited by W. M. Linfield, published by Marcel Dekker, Inc., New
York, 1976, and "Cationic Surfactants", edited by E. Jungermann,
Marcel Dekker, Inc., New York, 1976. Both of these references are
incorporated by reference for their disclosures in this regard.
The electronically conducting polypyrrole or copolymers of pyrrole
of the present invention are prepared by electropolymerization of a
pyrrole or a co-polymerizable mixture containing a pyrrole at an
electronically conductive surface in an electrolytic bath. The
electrolytic bath contains a pyrrole or mixture of pyrrole and
co-polymerizable monomer, at least one electrolyte salt which
includes an anion which will be incorporated into polymer upon
formation and at least one liquid in which the pyrrole (and/or
co-polymer) and electrolyte salt together have some finite
solubility. The bath may additionally contain a second non-miscible
liquid or a gas or finely divided solid particles or combinations
thereof. In one embodiment, the electrolytic bath comprises a
pyrrole or co-polymerizable mixture of pyrrole and water. In
another embodiment, the electrolytic bath comprises the pyrrole or
co-polymerizable mixture of pyrrole and an organic diluent. In yet
another embodiment, the electrolytic bath comprises the pyrrole or
co-polymerizable mixture containing pyrrole, water, and a
non-miscible liquid such as an organic diluent. The last embodiment
wherein the bath contains water and a non-miscible organic diluent,
hereinafter referred to as the two-phase system, is useful in
preparing compositions of the invention which may be characterized
as being porous and having very high surface areas.
The electropolymerization of a pyrrole or a co-polymerizable
mixture containing a pyrrole utilizing a two-phase system such as
water and an organic diluent comprises the steps of
A. immersing an electronically conductive surface in an
electrolytic bath comprising at least one liquid and at least one
non-miscible liquid wherein the pyrrole or co-polymerizable mixture
is one of the liquids or is dissolved in at least one of the
liquids and
B. passing an electric current through said bath at a voltage
sufficient to electropolymerize the pyrrole or co-polymerizable
mixture containing a pyrrole at the electronically conductive
surface. Preferably, one of the liquids is water and the
non-miscible liquid is an organic diluent. Examples of organic
diluents useful in the present invention include organic
hydrocarbons such as aliphatic or aromatic hydrocarbons,
halogenated aliphatic or aromatic compounds, etc. specific examples
include mineral spirits, hexane, heptane, toluene, xylene,
1,2-dichloroethane, dichloromethane, carbon tetrachloride, and
chlorobenzene.
The amount of the pyrrole or co-polymerizable mixture containing
pyrrole in the electrolytic bath may vary over a wide range
although the total amount must exceed the amount necessary to form
the total amount of polymer desired. The amount of the pyrrole
dissolved in the electrolyte solution component(s) of the
electrolytic bath must be enough to permit a reasonable rate of
reaction. The amount will usually vary from about 10.sup.-3 molar
up to saturation of the electrolyte(s). The amount of electrolyte
salt in the electrolytic bath must be sufficient to both conduct
the current desired and provide sufficient anionic species for
incorporation into the polymer for the purpose of charge
neutralization. Typical concentrations are from 10.sup.-2 molar up
to saturation of the bath, and more typically 5.times.10.sup.-2 up
to 1 molar in at least one phase.
As mentioned above, the electrolytic bath of the invention may
contain other ingredients which provide desirable properties to the
compositions of the invention. Thus, the bath may contain low
mobility anions, plasticizers, redox couples, surfactants, etc., as
defined above. When an aqueous system or a multi-phase system
containing water is utilized for the electrolytic bath, an
emulsifier or emulsion stabilizer may be included to stabilize this
system.
The electronically conducting compositions contain at least one low
mobility anion, A, which has a strong tendency to be retained in
the composition on reduction.
Also useful herein are emulsion stabilizers such as the neutral
alkali metal salts of fatty acids having at least 12 aliphatic
carbon atoms in the fatty radical. These fatty acids include,
principally, lauric acid, stearic acid, oleic acid, myristic acid,
palmitic acid, linoleic acid, linolenic acid, behenic acid, or a
mixture of such acids such as are obtained from the hydrolysis of
tall oil, sperm oil, and other commercial fats.
Only a small amount of the stabilizer is necessary for the purpose.
It may be as little as 0.01 part and seldom exceeds 2 parts per 100
parts by weight of the electrolytic bath. In most instances it is
within the range from 0.1 to 3 part per 100 parts of the bath.
As mentioned, the electropolymerization process utilized in this
invention can be carried out in an organic diluent and more
particularly in an organic phase containing less than about 3% and
more preferably less than about 1% of water. Examples of organic
diluents include polyols, organic carbonates, ethers, nitriles,
etc. It is essential that the solvent does not undergo competitive
oxidation during the electropolymerization and thus interfere with
the polymerization or substantially reduce the current efficiency
of the polymerization process.
The electropolymerization of pyrroles from aqueous media, by either
a single-phase aqueous system or a multi-phase aqueous system is
possible. Many of the advantages of using aqueous systems are
apparent including, reduced costs, availability and easy
purification of water, the ability to utilize a wide range of ionic
materials as electrolyte salts in water, the ability to utilize
high concentrations of ionic species thus permitting high
electrochemical currents and high polymer formation rates. Under
controlled conditions, intact homogeneous films of polypyrroles can
be formed on a variety of substrates in aqueous media. Thicknesses
range from less than 100 Angstroms to a few millimeters for more
dense materials. In some instances, current density has an effect
on the morphology. The morphology of the electropolymerized
compositions of the invention can be further modified by the use of
the additives already discussed.
It has been observed that improved results are obtained when the
electroplating bath is thoroughly agitated during the
electropolymerization of the monomers. Agitation can be
accomplished by any known technique including vigorous stirring
with paddle mixers, magnetic stirrers, ultrasonics, vibration or by
bubbling gases through the bath to provide sufficient agitation
(including gases generated at the counter-electrode).
Electropolymerization is accomplished by passing an electric
current through the bath at a voltage which is sufficient to
electropolymerize the pyrrole or co-polymerizable mixture
containing a pyrrole at an electronically conductive surface
immersed in the electrolytic bath. The electric current may be a
continuous electric current or a varying electric current such as a
pulse current. Generally, the electric current is direct current
although in some instances alternating current may be useful.
The voltage at the anode should be sufficient to oxidize monomer
without producing significant changes in the bath, such as
degradation of a bath component, which would adversly affect the
polymerization. Generally, current densities of up to two amperes
per square centimeter may be used, but preferably, current
densities not exceeding 500 milliamperes per square centimeter are
utilized. The current density will be less than 250 and more
generally, less than 100 milliamps per square centimeter.
At the above current densities, the pyrrole or copolymerizable
mixture of a pyrrole is electropolymerized at the electronically
conductive surface. Depending upon the specific ingredients in the
plating bath, the electropolymerizable polypyrrole may either form
as a powder at the electronically conductive suface and fall into
and be dispersed in the electrolytic bath, or alternatively, be
deposited on the conductive surface. The deposit may be in the form
of a film which is either smooth and dense or irregular with less
than the bulk or theoretical density. Bulk or theoretical density
of the polymers is the density of continuous, pure polymer
containing no voids, pores, cavities or inclusions. The bulk or
theoretical density can usually be determined by floatation
methods. Examples of irregular deposits include porous films,
powders, dendriform materials, etc. The nature of the cation(s) as
well as that of the anion(s) present in the electrolytic bath
affects the electropolymerization. The morphology of the deposit on
the electronically conductive substrate can be controlled and
modified by the incorporation in the electrolytic bath of various
complexing agents for the ionic constituents of the electrolyte.
Examples of materials which function as growth regulators when
incorporated into the electrolytic bath include the above-discussed
non-ionic plasticizers (e.g. polyalkylene glycol such as
polyethylene glycol), cryptands, and commercially available crown
ethers such as 12-Crown-4, 15-Crown-5, and 18-Crown-6 available
from Aldrich Chemical Co.
The temperature of the electrolytic bath during the
electropolymerization process is generally maintained between about
15.degree. C. to about 50.degree. C., although polymerization
proceeds over a much wider temperature range. The reaction is
conducted at or about room temperature and preferably under
thermostatted conditions.
A variety of electronically conductive substrates that do not
undergo competitive oxidation during the electropolymerization can
be utilized in the process of the invention. Not all types of
metals can be used with the entire range of bath formulations. For
example, although steel surfaces are useful for electropolymerizing
pyrrole in the presence of sodium lauryl sulfate and water, the
electrolytic bath containing pentaerythrityl tetrasulfate and water
will not deposit a satisfactory film on steel, but deposits a
satisfactory coating on nickel substrates. The choice of particular
substrate material can be readily determined by those skilled in
the art, with a minimum of experimentation. The size and shape of
the substrate utilized in the process of the invention will vary
depending upon the type of cell in which the electropolymerization
process is conducted and on the desired form of the polymer. For
example, when flat films are desired, the substrate will be in
shape of a flat panel in a parallel plate cell.
A preferred embodiment provides for a rotating cylindrical anode or
a moving belt anode from which the polymer is removed in a
continuous process. The polymer can also be collected or stripped
from a stationary electrode in a continuous manner.
The time required to produce a given quantity or thickness of
polymer will depend upon several factors, including the current
density, bath temperature, size or physical dimensions of the
electronically conductive surface and the temperature of the
electrolytic bath. Moreover, the specific type of morphology
desired will be an important consideration when selecting the
values of the process variables such as temperature, current
density, time of coating, voltage, etc.
One of the advantages of the process, particularly with the aqueous
systems, is the ability to produce films of controlled thickness
over a wide range of thicknesses, and in particular, films having
thicknesses greater than 250 micrometers, and in particular,
thicknesses between a range of 0.5 mm. to 2 cm. Many prior art
processes have not been developed to the level required to produce
anything but thin films (200 micrometers or less).
In the general process of the invention, tthe electronically
conductive surfaces are introduced into the electrolytic bath and
connected to a current source. The polymer is formed at the anode.
The counterelectrode may consist of the bath tank or a separate
conductive surface(s) may be introduced into the electrolytic bath.
The bath may have a separate compartment for the secondary
electrode but the one compartment configuration is preferred.
When the electropolymerization process is completed, the substrate
is removed from the electrolytic bath, and the electropolymerized
material is mechanically stripped from the surface. This polymer
may be washed with water and with various non-aqueous solvents
(e.g., ethers, liquid hydrocarbons, etc.) to remove any undesirable
deposits contained on or in the material. If the deposited material
has not been fully dried, this can be achieved, if desired, by
heating the polymer at elevated temperatures, preferably under
vacuum. The particular temperatures will depend upon the nature of
the pyrrole or co-polymerizable mixture of pyrroles utilized in the
process, but will generally be less than 250.degree. C. and
preferably below 100.degree. C.
The following examples illustrate the process of obtaining the
polymer of pyrrole or copolymers of pyrrole:
Unless otherwise indicated, in the following examples,
electropolymerizations are conducted at 2 amperes for 30 minutes
using a Hanovia arc-lamp power supply controlled with a Variac.
Agitation is accomplished with a horizonal perforated glass disk
mounted on the bottom of a stirring rod (about 1 to 2 cm from the
bottom of the bath) and rapidly vibrated up and down with a
Vibro-Mixer (Model El, supplied by A.G. Fur Chemie-Apparatebau
Mannedorf-Zurich). The temperature is controlled with an ice bath.
Both electrodes are 15.times.7.5.times.0.05 cm panels of steel
(AISI No. 10/10) in parallel plate configuration that have been
degreased with toluene. The surface area (one side) of each
electrode immersed in the bath is 70 cm.sup.2 and the distance
between the electrodes is 5.5 cm. The polyethylene glycol used in
some of the examples has an average molecular weight of about
15-20,000. The bath is exposed to the atmosphere. The descriptions
of the polymer films of the following examples do not cover edge
effects. These effects produce irregularities which rarely affect
more than five percent of the total mass of the film.
EXAMPLE 1
In this example, the following components are utilized:
______________________________________ Grams
______________________________________ Pyrrole 40 Sodium Lauryl
Sulfate 40 Polyethylene Glycol 20 Distilled Water 1600 Heptane 200
(ml.) ______________________________________
The above first four ingredients are mixed in a container until
homogeneous, and 375 ml. of this mixture is added to the
10.8.times.8.9.times.5.7 cm. reaction vessel. Two steel panel
electrodes are put into place. Heptane (50 ml.) is added, and
agitation is accomplished mechanically with a Vibro Mixer.
Four films are separately prepared at 2 amperes utilizing a
reaction time of 30 minutes. The temperature is controlled with an
ice bath and is initially 21.degree. C. and rises to a temperature
of about 34.degree.-37.degree. C. during the reaction. The current
is maintained at 2 amperes, but the voltage changes from about 60
to about 40 volts during the course of the reaction. The
electrolyte side of each film has a few irregularities in the form
of dendriform projections (about 1 millimeter) and these
projections are removed by light abrasion before stripping the
films from the electrode surfaces. Each film is rinsed thoroughly
in distilled water and in heptane.
Two of the films are fully dried in a vacuum oven at 50.degree. C.
for 24 hours. The cleaned films obtained in this manner appear to
comprise 3 layers. The first layer which is the layer closest to
the steel panel is smooth and continuous. The second layer adjacent
to the smooth layer is a uniformly porous material and the third
layer adjacent to the second layer is denser and less porous than
the second layer. The two other films obtained in this example are
stripped of their backing or smooth layer and cut into 3/4 inch
strips. The strips are cleaned in a Soxhlet extractor with
distilled water for 15 hours. After drying at room temperature, the
pieces are further dried in a vacuum oven at 50.degree. C. for 24
hours.
EXAMPLE 2
A mixture of 5 grams of pyrrole, 1 gram of sodium ethane
disulfonate, 2 grams of polyethylene glycol and 200 grams of water
is prepared and added to an 8.times.7.times.4.5 cm reaction vessel.
The cathode is a 15.times.5.times.0.025 cm piece of Precision brand
shim steel (a product of Precision identified as NIDA/SIDA 1613D
Al). The anode is a 10.times.5.times.0.05 cm Nickel 200 panel.
(Nickel 200 is a product of Inco identified as a high purity
nickel.) The surface area (one side) of each electrode immersed in
the bath is about 40 cm.sup.2. Toluene (20 ml.) is added and the
mixture agitated using a Vibro-Mixer. The electropolymerization
reaction is conducted for 15 minutes at a constant current of 0.5
amperes at a potential of about 17 volts. The film formed on the
electrode is removed and observed to be a relatively porous uniform
film of about 0.3 to 0.4 mm in thickness.
EXAMPLE 3
A mixture of 20 grams of pyrrole, 4 grams of pentaerythrityl
tetrahydrogensulfate, 4 grams of polyethylene glycol and 800 grams
of water is prepared and mixed until homogeneous. A volume of 375
ml. is added to a 5.7.times.8.9.times.10.8 cm reaction vessel, and
50 ml. of dichloromethane also is added to the vessel. In this
example, a panel of steel (AISI No. 10/10) (15.times.7.5.times.0.05
cm) is used as the cathode, and a Nickel 200 sheet
(14.2.times.7.6.times.0.025 cm) is used as the anode. The
electropolymerization is carried out in a normal manner over a
period of 15 minutes while maintaining a current of 2 amperes. A
porous mass of approximately 1 cm in thickness with a low density
(less than 0.1 g cm.sup.-3) is obtained; this porous mass is
electronically conducting.
EXAMPLE 4
A mixture of 20 grams of pyrrole, 10 grams of sodium-1,10-decane
disulfonate, 10 grams of polyethylene glycol and 800 parts of water
is prepared, and 375 ml. added to each of two reaction vessels.
Heptane, (50 ml) is added to each reaction vessel, and the
electropolymerization carried out in the normal manner at a current
of 2 amperes. The electropolymerization in the first reaction
vessel is terminated after 5 minutes yielding a thin black
electronically conductive film covered with small dendriform
projections of about 1 mm. in height.
The electropolymerization reaction in the second vessel is carried
out for 39 minutes yielding a thicker base film covered with small
dendriform projections of approximately the same dimensions as for
the previous film.
EXAMPLE 5
A mixture of 10 grams of pyrrole, 10 grams of sodium lauryl sulfate
and 0.5 grams of polyethylene glycol is prepared and added to the
reaction vessel. In this example, both electrodes are steel panels
and agitation is by a Vibro Mixer. The electropolymerization
reaction is conducted for 20 minutes at a current of 2 amperes. A
thick rather uniform coating is deposited on the anode and the
coating is covered with small dendriform shapes which are easily
removed by light abrasion.
EXAMPLE 6
The procedure of Example 5 is repeated except that 50 ml of heptane
is added to the mixture in the reaction vessel, and the
electropolymerization is conducted for five minutes at 2 amperes.
The film prepared in this manner is more porous than the material
obtained from the procedure of Example 5 and is covered with
dendriform shapes.
EXAMPLE 7
Pentaerythrityl tetrasulfate ammonium salt is prepared from
pentaerythritol and sulfanic acid in N,N,-dimethylformamide. A
mixture of 5 grams of pyrrole and 5 grams of the ammonium salt in
200 ml. water is prepared and electropolymerized in a
8.times.7.times.4.5 cm reaction vessel wherein the cathode is a
15.times.5.times.0.025 cm nickel sheet. About 40 cm.sup.2 of the
nickel sheet is immersed in the bath. The distance between
electrodes is 4.5 centimeters. Electropolymerization is conducted
at a current of 0.3 amperes for a period of 10 minutes yielding a
black electronically conducting film characterized by a somewhat
rough surface on the solution side of the film.
EXAMPLE 8
The procedure of Example 7 is repeated except that 2 grams of
polyethylene glycol is included in the mixture contained in the
reaction vessel. The black electronically conducting film obtained
in this manner is more uniform and smoother on the solution side
than the film obtained in Example 7.
EXAMPLE 9
Mannityl hexasulfate ammonium salt is prepared from mannitol and
sulfamic acid in dimethylformamide. A mixture of 5 grams of pyrrole
and 1 gram of this ammonium salt is dissolved in 200 ml. of water.
Utilizing the apparatus described in Example 7, the polymerization
is carried out at a current of about 0.4 amperes over a period of
20 minutes. The product is a black electronically conducting film
which is shiny on the substrate side and rough on the solution
side.
EXAMPLE 10
The procedure of Example 9 is repeated except that 2 grams of
polyethylene glycol is added to the mixture in the reaction vessel.
A more uniform film is obtained in this example which is much
smoother on the solution side.
EXAMPLE 11
A mixture of 15 grams of pyrrole in 500 grams of water is prepared,
and a second mixture of 10 grams of potassium ferricyanide and 5
grams of polyethylene glycol is prepared in 400 ml. of water. The
two solutions are mixed together and shaken. Approximately 450 ml.
of the mixture is poured into the 10.8 .times.8.9.times.5.7 cm
reaction vessel. The electrodes used in this example are both steel
panels. The electropolymerization is conducted at 5 amperes. At the
start of the reaction, the temperature is 23.degree. C. and the
voltage is 22 volts. During the electropolymerization reaction, the
temperature is stabilized at 31.degree.-32.degree. C. with an ice
bath. At this temperature, 20 volts is required to maintain a
current of 5 amperes. The distance between electrodes is 5.5 cm.
The electropolymerization reaction is conducted for 40 minutes. The
polymer is then removed from the anode. This film is 0.8 mm. thick,
black and electronically conducting. The film is smooth on both
sides although smoother on the substrate side.
EXAMPLE 12
The procedure of Example 11 is repeated except that the
15,000-20,000 molecular weight polyethylene glycol is replaced by
an equivalent weight of Carbowax 4000 (a product of Union Carbide
identified as 4,000 molecular weight polyethylene glycol). The
electropolymerization reaction is conducted at 5 amperes current
and about 20 volts are required to maintain this current throughout
the 40 minute reaction period. The temperature of the bath ranges
from 22.degree. to 32.degree. C. The polymer is removed from the
electrode, and the film obtained in this manner is black and
electronically conducting. The substrate side is smooth while the
solution side is covered with dendriform structures.
EXAMPLE 13
A mixture of 2 grams of pyrrole, 0.4 grams of a 50% aqueous
solution of the sodium salt of 2-acrylamido-2-methylpropanesulfonic
acid and 100 ml. of water is prepared and mixed until homogeneous.
In this example, the cathode of the reaction vessel is a platinum
strip (0.5.times.3 cm.) and the anode is a gold surface (2.times.4
cm) with about 4 cm.sup.2 immersed in the bath. The electrodes are
rinsed with distilled water prior to use. The electropolymerization
in this example is carried out using a Hewlett Packard power
supply/amplifier Model 6824A. The electropolymerization reaction is
conducted at a current of 24 milliamps and at a voltage of 15 volts
for a period of 2 minutes. A thin black electronically conductive
film is deposited on the gold surface.
EXAMPLE 14
The procedure of Example 13 is repeated except that the electrolyte
salt utilized in poly(2-acrylamido-2-methylpropanesulfonic acid
sodium salt having an inherent viscosity of 0.1 dl. g..sup.-1
(measured in 0.5 N NaCl at 30.degree. C.). The
electropolymerization is conducted at 30 milliamps at 20 volts for
a period of 2 minutes. A smooth thin glossy black electronically
conducting film is deposited on the gold surface.
EXAMPLE 15
A mixture of 20 grams of pyrrole, 20 grams of sodium lauryl
sulfate, 10 grams of polyethylene glycol and 800 grams of water is
prepared, and 375 ml. of this mixture 800 grams of water is
prepared, and 375 ml. of this mixture is added to the
10.8.times.8.9.times.5.7 cm reaction vessel. Heptane (50 ml) for
each experiment is then added to the reaction vessel, and agitation
is accomplished with a rapidly vibrating glass disk. The
temperature is controlled with an ice bath. In this example, the
electropolymerization is carried out using a current of 2 amperes.
The reaction time is 30 minutes and the reaction temperature ranges
from 20.degree.-38.degree. C. The polymer formed on the anode is
removed and cleaned by washing several times in distilled water.
The film prepared in this manner comprises a very thin base layer
next to the substrate, a uniformly porous layer adjacent the base
layer and a denser wrinkled less porous layer on the electrolyte
side. The polymer layer is removed from the electrode and a
4.times.1 cm strip is cut from the film and its thin base layer is
removed. The rest of the film is broken into pieces and rinsed
several times with distilled water along with the strip. The pieces
and the strip are then rinsed further in a Soxhlet extractor using
distilled water for 15 hours (about 40 extractions). The materials
are then dried in a vacuum oven at 80.degree. C. for 29 hours. This
polymer is electronically conducting and can be ground dry to a
porous powder which is easily cold pressed without any additives
into various shapes as desired. The shapes obtained in this manner
are also electronically conducting.
EXAMPLE 16
The procedure of Example 15 is repeated except that the mixture
contains only 7.5 grams of polyethylene glycol. The
electropolymerization of the mixture results in a thinner, denser
film than obtained in Example 15. The film also does not appear to
be as flexible and the corresponding powder does not cold press as
well as the powder obtained in Example 15.
EXAMPLE 17
The procedure of Example 15 is repeated except that the mixture
contains only 5 grams of polyethylene glycol. The film obtained in
this manner is electronically conductive, is thinner than the film
obtained in Example 16 and is less uniform.
EXAMPLE 18
An electrolyte bath is prepared comprising 1 g of phenyl phosphonic
acid and 2 g of pyrrole in 100 g of water. The
electropolymerization is carried out in the unstirred bath on a
gold strip of dimensions 3 cm.times.0.5 cm. The gold strip is
immersed to a depth of 1 cm. A platinum counter-electrode is
employed and a current of 1 milliampere is maintained for 300
seconds. The product is a black electronically conducting film.
EXAMPLE 19
A mixture of 40 grrams of pyrrole, 40 grams of sodium lauryl
sulfate, 15 grams of polyethylene glycol and 1,600 grams of water
is agitated until homogeneous, and 1200 ml is added to a
8.25.times.14.times.19 cm plastic reaction vessel. Both electrodes
are 14.times.19.times.0.1 cm panels of steel (AISI No. 10/10 steel
plate degreased with toluene. Heptane (150 ml) is added and
agitation is accomplished with a Vibro Mixer. The surface area of
the anode covered with polymer is about 250 cm.sup.2. The
electropolymerization reaction is conducted for a period of one
hour at a current of about 4 amperes D.C. The product is removed
from the anode and partially pulverized by hand while washing with
distilled water. After further washing (Soxhlet extraction with
distilled water) and drying, (vacuum oven, 85.degree. C., 20 hr.)
the polymer was pulverized further with a mortar and pestal. In
this manner, fine black electronically conducting powder is
obtained.
The powder obtained in this example can be cold pressed at room
temperature in the dry state without any additives, and the pressed
electrodes obtained in this manner exhibit improved electronic
conductivity over the dried electropolymerized films. The density
of the electropolymerized film is about 0.2 g cm.sup.-3 whereas the
density of the pressed electrode is about 0.8 g cm.sup.-3.
EXAMPLE 20
The procedure of Example 19 is repeated except that the power
source is a simple full wave rectifier (12 amp rating) controlled
with a Variac. The voltage requirements are essentially identical
to those of Example 19.
The electronically conductive polymers of co-polymers prepared
above are useful, for example, for electrodes in electrochemical
cells (e.g., as electrodes in batteries, both primary and secondary
batteries); as coatings for photocells to inhibit photo-corrosion
or corrosion processes; for catalytic electrodes; for electric
conductors; for conductive substrates and/or binders and mixtures
for composite electrodes; for switching devices; and as durable or
corrosion resistant electropolymerized coatings. The electronically
conductive polymers are also useful in solid state applications
(e.g., in the formation of junctions) and/or for photovoltaic and
photoelectrochemical devices and as reversible electrode materials
in electrochemical cells and batteries.
The polymer of pyrrole or copolymer of pyrrole when obtained from
electrodeposition is conveniently removed from the electrode by
scraping or mild agitation. Where the free radical method is used
to generate the polymer of pyrrole or copolymer of pyrrole, the
mixture may be stripped of excess solvent, reactant and other
materials and thereafter treated with the strong base in order to
substantially increase the surface area. Of course, where the
electrochemical method is utilized, the scraped material may be
washed, otherwise prepared and thereafter treated in a suitable
solvent with the strong base to remove the counter anion thereby
substantially increasing the surface area.
The next aspect of the present invention discusses the
deprotonation of the polymer of pyrrole or co-polymer of pyrrole.
It will be observed that when using the electochemical method, an
anion of an organic material, typically, a lauryl sulfate anion
will be associated with the polymer of pyrrole or co-polymer of
pyrrole. When the peroxygen method is employed, an anion such as
KSO.sub.4.sup.- is intimately associated with the polymer of
pyrrole or co-polymer of pyrrole.
It has been determined that the anion associated with the polymer
of pyrrole or co-polymer of pyrrole may be removed utilizing a
strong base. By a strong base, it is intended to exclude such weak
materials which cannot effectively remove substantially all of the
anion associated with the polymer of pyrrole or co-polymer of
pyrrole. Suitable materials which may be utilized to remove the
anion include materials such as the alkali metal and alkaline earth
metal hydroxides, the alkali metal and alkaline earth metal
alkoxides, and various amine bases. The alkali metal hydroxide of
choice is sodium hydroxide. However, potassium hydroxide, lithium
hydroxide or even cesium hydroxide may be utilized to remove the
anion from the polymer of pyrrole or co-polymer of pyrrole. Among
the alkaline earth metal hydroxide which may be utilized, it is
suggested that calcium hydroxide is most convenient from a cost
effective standpoint. However, material such as magnesium hydroxide
may also be utilized effectively to remove the anion from the
polymer of pyrrole or co-polymer of pyrrole.
The alkoxides utilizable herein are any of the conventional
alkoxides such as sodium or potassium methoxide. Of course, the
methoxides are typically utilized in mixture with the alcohol
corresponding to the alkoxide moiety. The solvent utilizable for
removing the anion when a water-soluble base is utilized is
conveniently water. It is, of course, however, possible to use
mixtures of various solvents to obtain a greater effect in removal
of the anion.
A concomitant effect of removing the anion from the polymer of
pyrrole or co-polymer of pyrrole is to remove the acidic proton
which is associated with a charged pyrrole ring. As the polymer of
pyrrole or co-polymer of pyrrole is now deficient in a proton, the
corresponding nitrogen atom on the polymer has an unshared electron
pair. The deprotonated polymer then becomes a Lewis base thereby
making it possible to associate any of several Lewis acids or
Broensted acids species within the polymer matrix.
The polymer matrix is also useful in that the unshared pair of
electrons on a nitrogen atom within the polymer of pyrrole or
co-polymer of pyrrole may be covalently bonded to another species
to provide an additional catalytic usage of the deprotonated
polymer of pyrrole or co-polymer of pyrrole.
Suitable materials which may be bound into the matrix of the
polymer of pyrrole or co-polymer of pyrrole include metallic
catalysts such as transition metals or metallic ions such as
ferric, ferrous, cupric, cuprous, manganic, nickel, osmium,
ruthenium or aluminum or mixtures of the foregoing materials. Where
a metallic cation is used, any appropriately associated anion may
be present in the molecule. The catalyst support system is
extremely effective because of the number of catalyst support sites
that it provides on the pyrrole backbone. It is desirable that any
associated ligands with the metallic species not be so large as to
preclude other sites on the polymer of pyrrole or co-polymer of
pyrrole from being blocked for usage.
Lewis acids which may be used as catalysts may also be introduced
into the polymer of pyrrole or co-polymer of pyrrole following its
deprotonation. Such catalytic materials include compounds such as
bromine, iodine, boron trifluoride or sulfur trioxide or mixtures
thereof.
It is also possible to reprotonate the deprotonated polymer of
pyrrole or copolymer of pyrrole. It might be first asked why one
would be interested in reprotonating a material which is protonated
in its manufacture. The answer to this question is that it is
possible to obtain a more active catalytic system by preparing the
material such as by the electrodeposition method previously
described, and subsequently treating the material as hereafter
described. That is, the polymer of pyrrole or copolymer of pyrrole,
following its electrochemical production with a material such as
sodium lauryl sulfate included therein provides a material having a
far greater surface area following removal of the lauryl sulfate
anions. However, when reprotonating the polymer of pyrrole or
copolymer of pyrrole with a material such as a mineral acid, it is
possible to thereafter obtain a material having an extremely high
surface area which is a protonated polymer of pyrrole or copolymer
of pyrrole. Such acids as dihydroquinone sulfonic acid can be
incorporated into the deprotonated polymer by mixing the acid in a
solvent such as methanol. The dihydroquinone sulfonic acid is
unstable under the conditions of electropolymerization and thus
direct incorporation during polymerization is not possible.
Suitable materials which may be used to reprotonate the polymer of
pyrrole or copolymer of pyrrole include any of the non-oxidative
acids. Thus, mineral acid such as phosphoric, sulfuric or
hydrochloric acids are suitable to reprotonate the polymer of
pyrrole or copolymer of pyrrole. Organic acids such as quinone
sulfonic acid or methane sulfonic acid may also be used to
reprotonate the polymer of pyrrole or copolymer of pyrrole. In any
event, the amount of acid employed is usually a slight excess over
that required to completely associate a proton with the unpaired
electron on the nitrogen atom. The slight excess of the acid is
utilized for convenience considering the cost of polymer of pyrrole
or copolymer of pyrrole.
The degree with which the polymer of pyrrole or copolymer of
pyrrole is reprotonated is also a matter of choice directed to the
eventual utility of the polymer of pyrrole or copolymer of
pyrrole.
It is desirable that an acid such as nitric acid not be utilized,
in that nitric acid can attack the polymeric backbone of the
polymer of pyrrole or copolymer of pyrrole. Accordingly, any acid
may be used to reprotonate the polymer of pyrrole or copolymer of
pyrrole providing it does not substantially destroy the polymer
backbone.
The following are examples of the present invention.
EXAMPLE A
A sample of a polymer of pyrrole corresponding to unsubstituted
pyrrole which has a surface area of approximately 15 square meters
per gram is obtained according to Example 1. The polypyrrole at 0.1
equivalents is placed in a glass reaction vessel which is sealed
from the atmosphere. The polypyrrole has an equivalent weight of
509. Also added to the reaction vessel is 0.12 equivalent of
potassium methoxide. Excess methanol provides additional solvent
for the reaction. The potassium methoxide is extremely effective in
removing protons from the polymer.
The reaction is maintained as close to 20.degree. C. as is
practical. The reaction is allowed to continue for a period of
approximately 12 hours. Following this period of time, the
deprotonated polypyrrole is filtered and washed in additional
methanol.
Following the filtration and washing in methanol, the deprotonated
polypyrrole is placed in an Soxhlet extractor for approximately 14
hours.
The deprotonated polypyrrole as obtained above has a surface area
of approximately 50 square meters per gram.
EXAMPLE B
An aqueous mixture of 50.9 parts polypyrrole, and 1000 parts water
from Example 1 is introduced to a sealed glass reaction vessel. The
anion of the polymer is lauryl sulfate. The polypyrrole lauryl
sulfate has an equivalent weight of 509. Potassium hydroxide (5.72
parts) is introduced to the aqueous mixture incrementally to
provide an even reaction rate. The temperature of the reaction is
maintained as close to room temperature as is possible.
The deprotonated polypyrrole is filtered, and washed in methanol,
followed by stripping and drying of the filtrate. The deprotonated
polypyrrole polymer is then dried in a vacuum oven.
EXAMPLE C
Polypyrrole is used as a support for copper by obtaining a
polypyrrole which has been deprotonated according to Example A.
Deprotonated polypyrrole in the amount of 5 parts is placed in a
reaction vessel and 0.66 part of cupric chloride is added. The
mixture is refluxed for five hours to obtain a copper complexed
polypyrrole. The copper complexed polypyrrole is useful as an
anti-oxidant catalyst to reduce peroxide.
EXAMPLE D
Polypyrrole which has been deprotonated according to Example B is
reacted to give a polypyrrole complex of manganese suitable as a
catalyst.
The deprotonated polypyrrole is reacted in an equivalent amount
with manganese chloride.
The ingredients are placed in a glass reaction vessel and
maintained at reflux under back pressure, of nitrogen for a period
of approximately 5 hours. Following the 5 hour time period, the
product is washed in methanol and dried in a vacuum oven. The
product obtained is suitable as a manganese catalyst.
EXAMPLE E
Polypyrrole obtained from Example A is reacted with iodine to
obtain an iodine polypyrrole complex.
Five parts of polypyrrole polymer obtained as above are added to
three parts of iodine in 70 parts of methanol. The reaction is
continued with heating to reflux for a period of 5 hours.
The iodine polypyrrole complex is then washed in methanol and then
dried in a vacuum oven. The catalyst obtained from this example is
useful as a Lewis acid catalyst.
EXAMPLE F
A polymer obtained according to Example A is utilized at 5 parts to
4.1 parts of nickel acetate tetrahydrate. Potassium carbonate in
the amount of 2.2 parts is added to a glass reaction vessel which
contains 60 parts of nitrobenzene. All the reactants are placed in
the glass reaction vessel and heated to 120.degree. C. The
temperature is adjusted to 100.degree. C. after the reaction has
been initiated. The reaction mixture is held at 100.degree. C. for
approximately 5 hours.
The nickel doped polypyrrole polymer obtained in the present
Example is then successively washed in nitrobenzene, methanol and
water. This product is then filtered and dried.
The nickel catalyst obtained herein is suitable as an oxidation
catalyst.
EXAMPLE G
The boron trifloride adduct of a polypyrrole polymer is obtained in
the following fashion. The polypyrrole is obtained as in Example A.
Boron trifluoride (BF.sub.3) is bubbled through toluene in a glass
reaction vessel containing the deprotonated polypyrrole. The boron
trifluoride is added over a period of about two hours at 20.degree.
C. The reaction vessel is then evacuated by purging with nitrogen
gas for approximately one hour.
The reaction product so obtained is then washed in toluene,
followed by an ether washing, filtration and drying.
The boron trifluoride reaction product of the polypyrrole polymer
is useful as an alkylation catalyst.
EXAMPLE H
This example desribes the reprotonation of a deprotonated
polypyrrole.
Deprotonated polypyrrole (5 parts) is placed in a flask containing
50 parts of distilled water. With stirring at room temperature, 5
parts of concentrated hydrochloric acid are added over 30 minutes.
The product is stirred at room temperature for 2 hours, then
filtered and washed 3 times with distilled water. After drying in
vacuo at 80.degree. C. for 4 hours, 5.1 gms of a black, conducting
polymer is obtained. Chloride analysis is 13.3% indicating
incorporation of the proton as the hydrochloride salt of the
polymer. The product has conductivity of 1 S cm.sup.-1.
EXAMPLE J
Into a clean, dry 500 ml roundbottom flask is placed 250ml of
anhydrous diethyl ether. Thereafter 2.0 gms of anhydrous iron (III)
chloride is added. The mixture is slurried to obtain a solution of
the iron salt. To this solution is slurried 3.0 gms of deprotonated
polypyrrole from Example A. The solution is then stirred for 3
hours at room temperature. The black powder is then filtered and
washed 3 times with 50 ml aliquots of anhydrous diethyl ether. The
product is dried at 80.degree. C. under 1.32 KPa vacuum for 5
hours. Analysis of the powder shows 4.07% chloride and 3.01% iron
by weight in the iron laden polymer.
EXAMPLE K
Deprotonated, iron-containing, polypyrrole from Example J is heat
treated at 800.degree. C. under an inert atmosphere (Argon) for 2
hours. This material is then tested in a ring and disk apparatus
for oxygen-reduction catalytic activity according to the following
procedure.
The oxygen reduction experiments are conducted with thin layer
Teflon-bonded carbon electrodes. These electrodes are prepared by
placing 25 mg of the deprotonated, iron containing polypyrrole
powder in a small beaker. Distilled water is then added to the
powder and the mixture agitated in an ultrasonic bath for about 30
mintues. Subsequently, a few ml of a dilute suspension of a Teflon
emulsion (Dupont T 30B, 60% Teflon in water plus 7% Triton X-100 as
a stabilizer) are added to the polypyrrole/water mixture without
interrupting the agitation. The amount of Teflon used is sufficient
to yield 10% w/w of Teflon in the polypyrrole matrix. This material
is then filtered, kneaded with a spatula onto a Teflon sheet, and a
small amount (2.5-3 mg) is applied onto a slightly recessed (0.1 ml
deep) ordinary pyrolytic graphite disk of an otherwise conventional
ring-disk electrode assembly. The surface is smoothened using a
spatula so as to create a common plane with the rest of the
electrode front end.
The oxygen reduction test is run at 20.degree. C. in 0.1 M NaOH
saturated with oxygen gas. The ring and disk procedure shows
catalytic activity for oxygen reduction when compared to electrodes
fabricated from carbon. A general discussion of electrode
fabrication is found in J. Electroanal. Chem., 184 (1985) pp
419-426.
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